The priest is only the instrument or minister. The atonement s Jesus’ atonement. Dear friend, some of our protestant friends have misconceptions so are not the best teachers of our Catholic truth. Maybe you could source the Vatucan Two documents to see what the Catholic teaching is. I don’t still have copies, but you should be able to find copies.
For “Christ has come, as the great high priest of all blessings…and offered Himself as the perfect sacrifice to God through the eternal Spirit [purifying] our inner self from dead actions so that we do our service to the living God. He brings a new covenant, as the mediator, only so that the people who were called to an eternal inheritance may actually receive what was promised: His death took place to cancel the sins that infringed the earlier covenant.” [Hebrews 9:11, 14-15]
“The One that offers Sacrifice is the same One who, after having sacrificed himself on the Cross…to obtain for us eternal redemption…offers Himself now by the ministry of the priest; there is no difference except in the manner of offering.” [Council of Trent, S. 22, c.2] “For in it Christ perpetuates in an unbloody manner the sacrifice offered on the Cross, offering Himself to the Father for the world’s salvation through the ministry of priests.” [Vatican Two documents]
“The Eucharistic Sacrifice is the source and summit of the whole of the Church’s worship and of Christian life. The faithful participate more fully in the sacrament of thanksgiving, propitiation, petition and praise not only when they wholeheartedly offer the sacred Victim, and in it themselves to the Father with the priest, but also when they receive this same Victim sacramentally.” [Vatican Two documents]
“The other sacraments, as indeed every ministry of the church and every work of the apostolate, are linked with the Eucharist and are directed towards it. For the Eucharist contains the entire spiritual good of the Church, namely, Christ Himself, our Passover and living bread, offering through His flesh, living and life-giving in the Spirit, life to all who are thus invited and led on to offer themselves, their labours, and all created things together with Him.” [Vatican Two documents
“The faithful are gathered by the preaching of Christ’s Gospel and the mystery of the Lord’s Supper is celebrated, ‘so that through the Body and Blood of the Lord the whole brotherhood is united…Christ is present, by whose power the one, holy, catholic and apostolic Church is united. For the partaking has no less an effect than to change us into what we have received.’” [Vatican 11.9:7. Constitution of the Church, n.26]
“But union with Christ…is not to be limited to the duration of the celebration of the Eucharist; it is to be prolonged into the entire Christian life…(as) a continual thanksgiving under the Holy Spirit and may produce fruits of greater charity.” [Vatican Two documents]
God bless you, Trishie